tracing/histogram: Optimize division by constants
If the divisor is a constant use specific division functions to avoid extra branches when the trigger is hit. If the divisor constant but not a power of 2, the division can be replaced with a multiplication and shift in the following case: Let X = dividend and Y = divisor. Choose Z = some power of 2. If Y <= Z, then: X / Y = (X * (Z / Y)) / Z (Z / Y) is a constant (mult) which is calculated at parse time, so: X / Y = (X * mult) / Z The division by Z can be replaced by a shift since Z is a power of 2: X / Y = (X * mult) >> shift As long, as X < Z the results will not be off by more than 1. Link: https://lkml.kernel.org/r/20211029232410.3494196-1-kaleshsingh@google.comSuggested-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Kalesh Singh <kaleshsingh@google.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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